1. Field of the Invention
The present invention relates to an Ethernet network or the like and, more particularly, to a technique for keeping track of virtual LAN topology set up on the Ethernet network.
2. Description of the Related Art
When telecommunications carriers and the like (type one telecommunications carriers which are generally termed carriers) that possess their own infrastructures required to provide services provide communications services, it is general practice to organize and operate multiple so-called virtual local area networks (LANs) in which nodes constituting their own Ethernet networks are logically grouped and allocated to companies which are their customers, using a virtual LAN technology (for example, IEEE 802.1Q). This kind of service is generally called a wide area LAN service or wide area L2 (layer 2) service.
FIG. 1 is a diagram showing an example of communications network infrastructure that a carrier possesses. In FIG. 1, the communications network 1 owned by the carrier is made up of nodes 10 denoted by small circles, links 12, each of which enables node-to-node communication, and an operation system 30 which administrates the entire communications network consisting of the nodes 10 and links 12. Combination of N and a number indicates a node ID and combination of P and a number indicates a port ID that is used for one node to communication with another node. For example, nodes N1 and N2 communicate through a port P1 of the node N1 and a port P2 of the node N2.
In the example of FIG. 1, the carrier logically sets up a virtual LAN 20-A with nodes N1 to N4 for company A and a virtual LAN 20-B with nodes N3 to N10 for company B.
Now, there will occur no problem as long as all configurations (settings) of these virtual LANs are performed by the operation system 30, but reconfigurations are sometimes performed by a person in charge at a node 10 not the operation system 30. In such an event, the operation system 30 may lose track of exact states of connections on the virtual LANs, as the virtual LANs management data supervised by the operation system 30 does not agree with actual configurations of nodes constituting the virtual LANs.
As prior art, ping and traceroute that are TCP/IP related utilities provide means for knowing node-to-node connectivity and nodes interconnections on the IP level. By applying techniques equivalent to the above utilities to the Ethernet level, it is possible to recognize bridge-to-bridge connectivity and bridge-to-bridge connections. However, to use these techniques, it is necessary to know the address (IP address or MAC address) of a target node. Therefore, these techniques are not useful in conditions where reconfiguration occurs with a node that is not exactly identifiable among the nodes constituting a virtual LAN like the above event. The IP address is an Internet Protocol address and the MAC address is a Media Access Control address.